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Wrought Iron Shear steel question


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After reading the thread on "heat treating shear steel", I just HAD to try making some. I

 

forged out five strips of wrought iron (old anchor chain), about 3/32 inches thick each,

 

and stacked them with, and wrapped them with strips of leather, into a nice neat bundle.

 

This bundle went neatly into a "can" and I sealed the end with Satinite. I cooked it at

 

about 1,900 degrees F for 1 1/2 hours. When I opened the can and extracted the pieces,

 

they were bright silver and sparked similar to 1080. I stacked the five pieces and forge

 

welded them up, folded twice and then drew out the blade. They welded easily. I

 

normalized three times (cooling in air), and then brought it up to temp and quenched in

 

oil, followed by a sub-critical anneal. I rough ground to 220 grit and did a clay coat -

 

quenched from about 1,500 degrees into warm brine. My test file felt a little bit sticky

 

on it, but it seemed to harden "okay". There was a weak hamon but it was too close to the

 

edge for my taste so I decided to do it again. This time I made the clay coat a little

 

thinner and kept it closer to the spine. I heated it to about 1,575 this time and quenched

 

in 120 degree brine. My test file would not bite the edge at all. I immediately could see

 

a strong hamon, so I cleaned it up, tempered it at 400 degrees for two 45 minute cycles and

 

began finishing.

After sanding down to 800 grit, I gave it a 40 second dip in FC and continued to finish to

 

1,000 grit. That is when I noticed the different texture of this steel. It looks "greasy"

 

- that is the best way I can describe it - greasy luster. Normally, by the time I get down

 

to 1,000 grit, the steel is looking pretty shiny and bright. This doesn't look that way.

 

Under 25X magnification, the surface looks like a sponge. Thousands of tiny, tiny pits,

 

some bigger than others, and about half of them filled with a hard, black substance that I

 

am presuming is the slag from the wrought. I don't have photo equip. to use with the

 

microscope, or I'd show a pic. I did photo the blade in bright sun - all the bright little

 

specs you see are either pits or inclusions. They are only visible like this in bright sun

 

- inside, with house lights the surface just looks greasy. Here is a link to the picture:mmilleroriginals.com

 

So, my question is - how do I avoid this? Would folding the steel more times squeeze out

 

more of the slag? Does anyone else out there have experience with this sort of thing?

 

I really like the sensitivity this material has to clay hardening and I plan to make more

 

of it. If there is something I can do in the making that will get around this one problem,

 

I'll be making lots more.

 

 

Michael

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i'm not sure that i'd change much...... that blade is sweet !

 

remember, wrought iron is much much different than regular iron.......it's never been melted, only reduced

-- with this in mind, i wouldn't expect it to ever look like regular steel

 

if you fold the wrought some more.....it should spread out the slags and make them finer looking in the metal......... I don't think at this point you can actually squeeze out anything.... .... maybe with more folds its possible to alloy it.. ( not sure on that )

 

with some of the muck bar that i get.... i used to fold it numerous times... then it really is hard to tell appart from mild.....

 

take care

Greg

 

ps.... very nice tutorial...... thanks !

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Thanks Greg. This is the first time I have attempted anything like this and I just didn't have any idea what to expect. What you said makes total sense to me. I guess I'll handle this one and put an edge on it and see how it performs / cuts.

Michael

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Cool Stuff!

 

Would another way to go about it be to weld-up the wrought, forge to rough shape THEN carburize? What are the advantages to carburizing before or after you weld and forge.

 

I'm thinking one might save some carbon loss from the welding heats by carburizing after you weld/forge to rough shape rather than carburizing before welding/forging the material ... would this work as well?

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Cool Stuff!

 

Would another way to go about it be to weld-up the wrought, forge to rough shape THEN carburize? What are the advantages to carburizing before or after you weld and forge.

 

I'm thinking one might save some carbon loss from the welding heats by carburizing after you weld/forge to rough shape rather than carburizing before welding/forging the material ... would this work as well?

 

Carburizing before you weld allows you to spread the carbon out more evenly. So the welding is a refining process. The carburized wrought iron is called blister steel before it is refine into shear steel. I hope this answers your question.

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You want to carburize small.thin pieces of wrought so the amont of carbon taken up by the iron is enough to be significant, the amount and depth of carbon up-take in this method is a function of time and temperature and it takes a bunch of time for an appreciable amount of carbon to get any distance into the surface of the iron. So essentially you get as much carbon as possible into the surfaces of the bars and then when it's all welded together and drawn out, hopefully the carbon diffuses throughut the iron enough that you get a piece of reletively "smoothed-out" steel.

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Ric left me with the impression that you had to go to about 2200 deg F, for 3-4 hours to get proper blister. You may have carburized the surface, but I'd be wary about how deep the carbon migration was on your bars.

 

Folding and welding does two things - 1, distributes the carbon more evenly throughout the billet, and 2, works out more impurities. Since the silicate content of WI is not a chemical bond, then getting it hot and working it several times will in fact drive them physically out of the material. I was whanging on some WI last night to prepare my attempt at blister, and at welding heat I was getting liquid silicate running down the bar and shooting across the shop when I hit it. Adding carbon wouldn't change that at all, and lowering the silicate content would be desirable in a blade. I'll get mine together tonight and report back tomorrow.

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Thank you all so much for your replies. After doing some cutting with this blade, it has become apparent that the carbon content was not as high as I thought it might be. After cutting only about a dozen linear feet of 8 oz leather, the edge would no longer shave hair. I am getting another batch ready, and will cook this one longer and at higher temp. I'll shoot for 3 hours at 2,200 degrees. The pieces of WI are quite thin - about 1/16 inch thick and one inch wide. I'm going to try to get 8 or 9 bars into the can. Thank you all again for your replies.

Michael

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I now need a thermocouple.

 

I overcooked it. I was worried I hadn't cooked long or hot enough, and ended up with half my pieces being over half gone, melted off the sticks. Bits in a puddle in the bottom of my crucible. If I can somehow weld all this together, I might have something, but I'm not hopeful.

 

I used charcoal powder, and I was amazed at how well it held up ... I still had black powder in the can when I was all done, mixed in with glowing hot metal. Amazing.

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has anyone gotten an analysis of some 18th century shear steel to see exactly what the carbon content is? most of the info i have read tends to lead to a RC hardness of less than 50 when hardened.and the historical process of cooking the wrought iron and carbon in a "can" for up to 3 weeks straight. anyone have more info?

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